1. Field of the Invention
This invention relates to a facsimile communication method and a facsimile machine, and in particular to a facsimile communication method and a facsimile machine for shortening the time of a protocol executed before transmission and reception of image information.
2. Description of the Related Art
Conventional facsimile machines execute facsimile communication in accordance with transmission control procedures standardized by ITU-T (old CCITT) Recommendations T.30 as a facsimile protocol on a public switched telephone network. However, in the transmission control procedures, a control signal is transmitted at a low speed of about 300 bps so that a distant office can receive the control signal reliably, and it takes time in protocols in phases A and B executed before transmission and reception of image information (phase C). Thus, hitherto, the following techniques for shortening the protocols in phases A and B have been proposed:
Disclosed in Japanese Patent Unexamined Publication No. Sho. 61-98064 is a technique wherein a polarity inversion detection circuit, a memory circuit for storing the telephone number and function of an associated machine, and a control signal sending circuit for sending a control signal for informing the associated machine of a simplified protocol are provided and to originate a call, the availability of the simplified protocol function of the associated machine is read from the memory circuit and if the associated machine has the simplified protocol function, a control signal (command signal spc) for notifying the associated machine of execution of a nonstandard simplified protocol is sent from the control signal sending circuit just after the polarity inversion detection circuit detects polarity inversion. However, the technique requires additional specific signal sending means for notifying the associated machine of execution of the nonstandard simplified protocol.
Disclosed in Japanese Patent Unexamined Publication No. Sho. 62-38660 is a technique wherein when a calling facsimile machine receives an NSF (nonstandard function identification signal) at 300 bps from a called party, it transmits an NSS (nonstandard function setting signal) at 300 bps, then successively transmits image information, thereby shortening the time of a TCF (training check signal) and a CPR (reception ready confirmation signal). The technique shortens the time of image information transmission as compared with the standard protocol. However, since the NSF and NSS are transmitted and received at 300 bps, it is likely that it will take significant time to transmit and receive the NSF and NSS under present conditions in which the communication function increasingly grows and accordingly the amount of data to be transferred by the NSF and NSS increases more and more, although it depends on the data amount of the NSF and NSS; the technique is inefficient.
In the techniques described in Japanese Patent Unexamined Publication No. Sho. 62-38660, since the calling party sends image information following the NSS, a fallback procedure does not exist; if image information training results in an error in the called party, a NACK signal (negative acknowledge) is sent to the calling party, which then again sends training and image information to the called party. However, since the calling party need not sense the NACK signal in the standard protocol, new means must be added, leading to an increase in costs.
Described in Japanese Patent Unexamined Publication No. Hei. 3-68262 is a technique wherein when a calling party detects a CED (called equipment discrimination signal) from a called party, it sends a tone and upon detection of the tone, the called party stops sending the CED and the calling party measures the CED length and if the measurement value is shorter than the threshold value, sends an NSS at high speed. However, since negotiation of a preprocedure is omitted and the calling and called parties communicate with each other according to communication parameters such as paper size, line density, compression method, etc., predetermined between both the parties, the functions that can be used with the standard protocol by changing the communication parameters cannot be used with the simplified protocol.
In the technique described in Japanese Patent Unexamined Publication No. Hei. 3-68262, the initial value of the communication speed of the NSS and image information transmitted following the NSS is predetermined and each time an error occurs, resending is performed. If the number of times an error has occurred reaches the specified number of times, the communication speed falls back, for example, from 9600 bps to 7200 bps for communication. However, in the technique, the calling party cannot recognize error occurrence in the called party and a mismatch may occur between the number of error occurrence times counted by the calling party and that counted by the called party. In this case, the calling and called parties differ in communication speed and the communication does not hold. Also, specific signal sending means for sending a tone for stopping sending the CED from the called party and notifying the called party of execution of the simplified protocol becomes newly necessary.
Further described in Japanese Patent Unexamined Publication No. Hei. 3-154566 is a technique wherein when polarity inversion is sensed, a 300-bps NSS is sent and if polarity inversion cannot be sensed and a CED is detected, a tone is sent for stopping the CED and a 300-bps NSS is sent. In the technique, the contents of the FIF (facsimile information field) of an NSF of an associated office are stored at the first communication time and at the next communication time and later, the NSF is omitted and communication parameters are determined based on the stored contents. For the image information communication speed, the calling party stores a communication speed history and transmits image information at the stored communication speed.
However, since the technique also transmits the NSS at 300 bps, it is likely that it will take significant time to transmit the NSS as in Japanese Patent Unexamined Publication No. Sho. 62-38660 described above; the technique is inefficient. In the technique, to omit transmission of the NSF from the called party, the calling party needs to store the contents of the FIF of the NSF of the called party at the time of first communication. To store the FIF contents for each associated party, a large-capacity memory is required, leading to an increase in costs.
The communication speed history needs to be stored because of no fallback procedure. To store the communication speed history for each associated party, a still larger capacity memory is required, leading to a further increase in costs. Also, specific signal sending means for sending a tone for stopping sending the CED from the called party and notifying the called party of execution of the simplified protocol needs to be newly provided, as in Japanese Patent Unexamined Publication No. Hei. 3-68262 described above.
Disclosed in Japanese Patent Unexamined Publication No. Hei. 3-205958 is a technique wherein a predetermined communication speed is set in the FIF of an NSF in a called party and the NSF is transmitted at 300 bps and a calling party transmits a fast NSS at the setup communication speed and subsequently also transmits framed image information. However, since the technique transmits the NSF at 300 bps, it is likely that it will take significant time to transmit the NSF as in Japanese Patent Unexamined Publication No. Sho. 62-38660 described above; this technique is also inefficient. Also described in Japanese Patent Unexamined Publication No. Hei. 3-205958 is that communication may be executed at the highest speed among the reception capabilities concerning the communication speed of the called party contained in the NSF or DIS in place of setting the communication speed in the FIF of the NSF. According to the description, when the called party transmits an NSF, next the calling party sends an NSS at high speed. If the highest speed of the calling party is slower than the called party, the called party, which does not contain means for sensing it, cannot sense the speed at which the calling party sends the NSS; there is a high possibility that communication will not hold.
Further in the technique, since the calling party sends image information following the NSS, a fallback procedure does not exist; described in Japanese Patent Unexamined Publication No. Hei. 3-205958 is that if an FCS error (frame check sequence error) occurs in the called party, the called party may send a tone for notifying the error occurrence and the calling party may resend the NSS at high speed. However, since the calling party need not sense such a tone in the standard protocol, new means must be added, leading to an increase in costs.
Further described in Japanese Patent Unexamined Publication No. Hei. 5-191613 is that while a called party sends a CED, a calling party sends a simplified protocol control signal and if the called party, which receives the simplified protocol control signal, stops sending the CED, then the simplified protocol is executed; if the called party does not stop sending the CED, a normal protocol is executed. However, specific signal sending means needs also to be newly provided for sending a simplified protocol control signal for stopping sending the CED and notifying the called party that the simplified protocol can be executed.
Described in Japanese Patent Unexamined Publication No. Hei. 5-219334 is a technique wherein when detecting a DED, the calling party sends a unique tone (DTMF) for also notifying the called party of the communication speed of image information to the called party for causing the called party to stop sending the CED and send a 300-bps NSF for a simplified protocol (NSF from which indispensable capability parameters are omitted). The calling party sends image information parameters at the fast communication speed notified with the unique tone before sending the image information. However, since the technique transmits the NSF at 300 bps, it is likely that it will take significant time to transmit the NSF as in Japanese Patent Unexamined Publication Nos. Sho. 62-38660 and Hei. 3-205958 described above; the technique is not much efficient. It is also necessary to newly provide unique tone sending means for sending the unique tone (DTMF).
Since the image information parameters are sent at high speed before the image information is sent, the information to be sent to the called party with the unique tone DTMF is only the communication speed of image information. However, no fallback procedure exists in the control and considering shortening of the communication time in the fallback procedure, it is necessary to speed up transmission and reception of the control signals such as an NSF. To shorten the communication time of image information, it is effective to apply the maximum communication speed 14.4 kbps defined in ITU-T Recommendations V.17, for example, for transferring the image information. To speed up transmission and reception of commands, the control signals may be transmitted and received at 14.4 kbps matching the above-mentioned image information communication speed.
However, to send the control signals, it is also necessary to send a training signal, etc., as defined in various recommendations. Since V.17 defines the training signal sending time as 1.2 seconds, if control signals are transmitted and received conforming to V.17, the training signal needs to be sent for a comparatively long time and the time required for transmitting and receiving the control signals is not necessarily shortened. Thus, the image information communication speed is not always the optimum communication speed for sending the control signals at high speed.